Technical Field
Exemplary aspects of the present disclosure generally relate to a scanning lens, a scanning device, such as a scanner, and an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof.
Related Art
In a scanning device for use in an image scanner, a facsimile machine, or a digital copier to scan a document image, a scanning lens forms a reduced optical image of the original image, and a solid-state image sensor, such as a charge-coupled device (CCD), images the reduced optical image and converts image data into an electronic image data.
To scan original data as color images, a so-called three-line CCD sensor including three light receiving elements with the respective filters for colors, such as red, green, and blue, is employed as the solid image sensor. The three-line CCD sensor forms a reduced optical image of the original onto the light receiving surface of the CCD sensor to perform color separation into three colors, thereby converting the color image data into electrical signals.
In the above-described scanning lens, there is a need for the image surface to have a high contrast in a high spatial frequency region and an aperture efficiency of approximately 100% up to the peripheral portion of the angle of view. In addition, to properly scan a color original document, there is a need for the image forming positions of the respective colors of red, green, and blue on the light receiving surface to coincide, with chromatic aberrations of the respective colors properly corrected.
Such a widely used scanning lens, known as a Gauss lens, provides a relatively large diameter and high resolution. However, to achieve the high performance required in recent years in the configuration of the Gauss lens, the number of lenses increases and the optical system also unavoidably increases in size as a result.